Wednesday, November 02, 2011

Two duct tales

kw: product testing, observations

I have had the ducts cleaned in two houses by two different methods, and they differ quite a lot. I haven't had rotary brush cleaning, which only works well if all the ducts are round. It also requires cutting into the plenum to attach a high-capacity vacuum, and we'll cover that in a moment. Both cleaning methods that we used rely on air blast to dislodge debris in the ducts, but they take quite different approaches: one relies on "air pull", the other on "air push".

At the first house, the operator used a truck-mounted vacuum, lots and lots of large-diameter tubing, and a separate air hose. The process was to take off the faceplate of a register or return duct and let the air pressure hold a faceplate with a large, soft gasket, at the end of the vacuum tube, against the hole. The air hose was inserted through a port in the faceplate. It ended in a foot-long flexible tube with a "pull" nozzle at the end. Such a nozzle has several holes directed backwards, toward the faceplate. When the high-pressure air is turned on, the flexible tube whips around, and the air blasts the loosened debris toward the faceplate and it is carried away to the vacuum on the truck. The backward-directed air blast also makes it easy to get the air hose all the way to the end of the duct. My job was to stand by the plenum and tell him (shout) when the end of the hose arrived. He would then increase the air flow and pull it back out, so each duct had a double going-over.

This method is for aluminum ducts only. The whipping hose with the nozzle is likely to crack or break fiberglass ducts. The only disturbance to the air system is the removal and replacement of faceplates. No cutting into the ductwork is needed.

Ten years later, in the house we presently live in, I had a quite different experience. I believe the cleaning was thoroughly done, but consider the process. The first step was to lug a large-capacity vacuum into my basement, cut a foot-square hole in the plenum, and attach the vacuum. Then, near the end of each duct, the operator drilled an inch-diameter hole into which he put an air hose with a push nozzle. He fed the hose in until it reached the vacuum, then turned on the vacuum and the air and pulled the hose back through the duct. The section of duct between the holes he drilled and the vents was reached by taking off the faceplate and using the air hose to blow debris toward the vacuum.

Once he finished all the supply ducts, the hole in the supply plenum was closed by duct taping the cut-out piece, and the process was repeated with the return air plenum. After that was finished and re-closed, he went around and put a piece of duct tape over each of the holes he'd drilled. This whole process made me rather anxious, and I've thought since that I should have not let it be done, but shopped around until I found someone who used the first method. It is less invasive of the whole system.

As I mentioned, the result was probably about the same, but I am much happier with the "air pull" method.